One construction of insulating glass units (IGU's) involves forming a spacer frame by roll-forming a flat metal strip, into an elongated hollow rectangular tube or “U” shaped channel. A desiccant material is placed within the rectangular tube or channel, and some provisions are made for the desiccant to come into fluid communication with or otherwise affect the interior space of the insulated glass unit. The elongated tube or channel is notched to allow the channel to be formed into a rectangular frame. A sealant is applied to the outer sides of the spacer frame in order to bond two glass panes or lites to opposite side of the spacer frame. Existing heated sealants include hot melts and dual seal equivalents (DSE). This system is not limited to these spacer frame types; other spacer frame technologies that are generally known in the industry can also be used with this system. The pair of glass panes are positioned on the spacer frame to form a pre-pressed insulating glass unit. Generally, the pre-pressed insulating glass unit is passed through an IGU oven to melt or activate the sealant. The pre-pressed insulating glass unit is then passed through a press that applies pressure to the glass and sealant and compresses the IGU to a selected pressed unit thickness. The completed IGU is used to fabricate a window or door.
It is known to construct triple pane IGUs having three panes or lites. Two outer panes contact spacer frames which separate the outer panes from a center or inner pane. When assembling an IG unit, it is important that the glass surfaces that are on the inside airspace remain uncontaminated for two reasons (1) preventing visual defects that cannot be cleaned and (2) preventing contamination of the perimeter of the glass which needs to remain clean or else the adhesive bond between the spacer seal and glass can be compromised ultimately leading to a seal failure.
GED, assignee of the present invention, currently manufactures an assembly system which conveys two lites of glass parallel to each other horizontally through a glass washer. One lite gets a spacer applied and the other passes through untouched. The two pieces of glass are conveyed and aligned onto a pair of vertical pivoting tables that bring the two pieces of glass together. The advantage to this system is that the glass surfaces that are on the inside of the IG are never touched by the conveyance system after the glass has left a glass washer, thus assuring the inside glass remains clean and contaminant free. This arrangement works very well for conventional dual glazed IG, but is not conducive for fabricating triple IG's. A current difficulty with assembling triple IG units is keeping all inside glass surfaces (Surfaces 2, 3, 4 & 5 on FIG. 4) contaminant free. With the current arrangement it is typical that the inner glass surfaces will make substantial contact with the conveyance system which presents a high risk of contamination of these surfaces.
Process Flow for Conventional (Dual) IG Units; FIGS. 1 & 3
                1. Lite A leaves a washer and is conveyed by conveyors 10, 12 to a spacer assembly station 20 where a spacer 22 gets applied to the sheet A.        2. Lite B leaves the washer and is conveyed down conveyors 30, 32, 34, 36 and waits for lite A.        3. When both lites are staged, conveyors move the corresponding lites to butterfly conveyors 40, 42.        4. The butterfly tables 50, 52 (FIGS. 12 and 13) pivot to vertical.        5. Glass or lite B on the conveyor 42 is pushed onto conveyor 40 against the lite having the spacer.        6. The butterfly tables pivot back to horizontal.        7. The assembled dual IG unit is conveyed out of conveyors 60, 62 and to an oven for downstream processing.        
This process flow is well established. Note that each conveyor set (i.e. two adjacent conveyors) are split into separate drive zones. This facilitates the ability to simultaneously process smaller IG's. If a sensor detects an IG over a certain length, in this case over 49″, only one IG is processed at a time.